1. Field of the Invention
This invention relates generally to the field of computer systems and, more particularly, to peripheral devices.
2. Description of the Related Art
The Universal Serial Bus (USB) allows coupling of peripheral devices to a computer system. USB is a serial cable bus for data exchange between a host computer and a wide range of simultaneously accessible devices. The bus allows peripherals to be attached, configured, used, and detached while the host is in operation. For example, a card reader for reading flash memory cards may be coupled to a host computer through the USB. USB based systems may require that a USB host controller be present in the host system, and that the operating system (OS) of the host system support USB and USB Mass Storage Class Devices. A USB hub may be coupled to a USB host controller to allow multiple USB devices to be coupled to the host system through the USB host controller. In addition, other USB hubs may be coupled to the USB hub to provide additional USB device connections to the USB host controller.
In recent years the electronics marketplace has seen a proliferation of appliances and personal electronics devices that use solid-state memory. For example, traditional film cameras have been losing market share to digital cameras capable of recording images that may be directly downloaded to and stored on personal computers (PCs). The pictures recorded by digital cameras can easily be converted to common graphics file formats such as Joint Photographic Experts Group (JPEG), Graphic Interchange Format (GIF) or Bitmap (BMP), and sent as e-mail attachments or posted on web pages and online photo albums. Many digital cameras are also capable of capturing short video clips in standard digital video formats, for example Moving Picture Experts Group (MPEG), which may also be directly downloaded and stored on personal computers (PCs) or notebook computers. Other devices that typically use solid-state memory include personal digital assistants (PDAs), pocket PCs, video game consoles and Moving Picture Experts Group Layer-3 Audio (MP3) players.
The most widely used solid-state memory devices include flash-memory chips configured on a small removable memory card, and are commonly referred to as flash-memory cards. The majority of flash-memory cards currently on the market are typically one of: Compact Flash™, MultiMediaMemory™ memory card (MMC) and the related Secure Digital Memory card (SD), SmartMedia™ memory card (SM), xD Picture CardS™ (xD), and Memory Stick™. Most digital cameras, for example, use Compact Flash™ memory cards to record images. Many PDA models use Memory Stick™ memory cards to hold data. Some MP3 players store music files on SM memory cards. Generally, data saved by PDAs and other handheld devices using flash-memory cards are also transferred or downloaded to a PC. In the present application, the term “flash-memory” is intended to have the full breadth of its ordinary meaning, which generally encompasses various types of non-volatile solid-state memory devices as described above.
Typically, a flash-memory card can easily be removed from the utilizing device. For example, a Compact Flash™ memory card can be removed from a digital camera much like film is removed from a standard camera. The flash-memory card can then be inserted into an appropriate flash-memory card reader coupled to a PC, and the image files directly copied to the PC. It should be noted that while a majority of smaller hand-held computers and PDAs have slots that receive Compact Flash™ memory cards, currently, most PCs do not, hence the need for a flash-memory card reader connecting to the PC. Most recently the preferred interface between flash-memory card readers and PCs has been the Universal Serial Bus, where the flash-memory card reader is connected to a USB port on the PC via a USB cable. Portable computer or notebook PCs typically also have PC-memory card (earlier known as Personal Computer Memory card International Association; PCMCIA) slots that, can receive PCMCIA memory cards configured as flash-memory card readers.
In all, the many different memory card formats present a wide array of interface requirements not only for PCs but for other digital systems as well, such as embedded systems. Different adapters are needed for each of the memory card formats. One solution to consolidate the interfacing of flash-memory cards to desktop and portable computer PCs has been the design and manufacture of multi-format flash-memory card readers that are capable of reading the most popular formats. Such memory card-readers are sometimes referred to as ‘Seven-in-one’ readers indicating that they may be used with the currently popular flash-memory card formats. As indicated above, such multi-format card readers are typically designed with a USB interface.
While USB devices, such as multi-format card readers and USB hubs designed with a USB interface, are typically connected to host PCs and/or notebook PCs via a USB cable, they may also be designed into computers as embedded USB devices. Typically, adding an embedded USB device, such as a card reader or hub, to a computer adversely affects power consumption of the computer. In general, a USB device attached to the USB host controller of the computer may prevent the central processing unit (CPU) of the computer from entering a low power state—e.g., the C3 state. The USB host controller, as a bus mastering peripheral, may keep the PCI bus active as long as it is attached to a USB device preventing the CPU from going into a low power state. This may especially be a problem for embedded devices (e.g., an embedded card reader). Unnecessary power may also be used to power a memory card that is not in use. When a memory card or multiple memory cards are inserted in a memory card-reader, they are normally fully powered as long as the memory card-reader is not in SUSPEND mode. In such case, the memory card can typically dissipate up to 100 mA, adversely affecting battery life.